Different types of light-based skin treatment devices are known that can treat different targets within the skin. These light-based devices use low or medium power light sources, like LED's, or relatively high power light sources, like IPL (intense pulsed light) and laser. With the low and medium power light sources certain targets within the skin, like fibroblast cells, can be stimulated to enhance the production of collagen tissue. Relatively high power light sources heat specific targets in the skin, like melanin, blood or water to induce local damages. These light-based skin treatments are dependent on the wavelength absorption profile of the selected target objects in the skin and are known as “selective photothermolysis”. Fractional laser treatment devices have the purpose of non-ablative fractional photothermolysis of the targeted skin tissue, in particular by heating the water in the targeted skin tissue, for example, to thermally denature the collagen tissue in the dermis. In these fractional laser treatments, laser pulses create microscopic treatment zones (MTZs) of thermally denatured skin tissue surrounded by thermally undamaged tissue. This boosts skin repair mechanisms and improves skin appearance. Denatured collagen will be replaced in time, typically between one and three months, by new collagen. This will result in a reduction of wrinkles and fine lines. As an additional benefit the cells in the epidermis are damaged and replaced within several days. This replacement of the epidermal cells will result in a more even skin tone and an overall increase of the radiance or glow of the skin. Furthermore, fractional skin treatment devices are known that are ablative in that they completely remove the tissue in the micro-zones. Currently these ablative devices are less suitable for home-use, but are used in professional environments. Light is not only used to treat skin tissue, but is also used to achieve temporary hair growth reduction. In this application a broadband IPL (intense pulsed light) flash is used to damage the hair follicle and stop or reduce the hair growth. In this application, selective photothermolysis is obtained by matching the IPL wavelength spectrum and the duration of the light flashes to the absorption spectrum and thermal relaxation time of melanin, which is present in a large amount in hair tissue. Furthermore, IPL can be used to reduce the visibility of pigmented spots.
Both above mentioned solutions are based on large aperture devices to efficiently treat relatively large areas of interest. However, there is a growing interest in devices that offer improved precision, for example pen-like devices, by means of which spot treatments are achieved. A pen-like device has often a relatively small tip. It is relatively difficult to design a device with such a small treatment tip that includes safety mechanisms providing a level of safety such that the device is suitable for home-use. The safety mechanism needs to prevent the skin treatment device from emitting a potentially unsafe intense light beam that may harm the human eye. It is common to all electronic devices to include an ON button which should be pressed by the user to enable a certain device component, e.g. turning on a light source. It is desired to have an additional safety mechanism.
Published patent application US2012/0323229 and, for example, also published patent application US2004/0176754 disclose safety means to detect whether a front side, having a light exit window, of a skin treatment device is close to or in contact with the skin. These safety means are, for example, based on a pressure sensor, mechanical switches or a reflectometer contact system or the like. Such safety means are relatively complex, and thus relatively expensive. When such safety means are to be miniaturized, these safety means become even more expensive and sensitive to damages.